Generally, an automatic document feeder has a function of automatically and successively feeding many paper sheets. The automatic document feeder is applied to a diversity of office machines such as multifunction peripherals, printers, faxing machines or scanners.
FIG. 1A is a schematic perspective view illustrating a conventional automatic document feeder. The automatic document feeder 1 as shown in FIG. 1A is applied to a printer. The automatic document feeder 1 comprises a sheet stopping mechanism 11, a sheet pick-up roller 12, a clutch gear 13, a belt 14, a motor 15, a big gear 16, an idle gear 17, a compound gear 18. The sheet pick-up roller 12 is used for transporting a paper sheet M into a sheet-feeding channel. The clutch gear 13 is used for driving rotation of the sheet pick-up roller 12. The belt 14 is driven to rotate by the motor 15. Upon rotation of the belt 14, the big gear 16 is rotated to simultaneously drive rotation of the clutch gear 13 and the idle gear 17. The compound gear 18 is rotated with the idle gear 17.
FIG. 1B is a schematic exploded view illustrating the sheet stopping mechanism of the automatic document feeder as shown in FIG. 1A. FIG. 1C is a schematic side view illustrating the automatic document feeder in a sheet-feeding status. The sheet stopping mechanism 11 comprises a swinging arm 110, a hollow ring 111, a coupling element 112 and a linking rod 113. In addition, plural elastic elements 111a are formed on the outer periphery of the hollow ring 111. The coupling element 112 is coupled with the hollow ring 111. The linking rod 113 is connected to the swinging arm 110 and a stopper 114. The swinging arm 110, the hollow ring 111 and the coupling element 112 are sheathed around an outer surface 181 of the compound gear 18. In a sheet pick-up status, the sheet pick-up roller 12 is rotated to transport the paper sheet M in a direction F (see FIG. 1C). Meanwhile, as the compound gear 18 is rotated, the elastic element 111a and a corresponding coupling element 112 are rubbed against each other to generate a friction force. Due to the friction force, the swinging arm 110 is swung, and thus the stopper 114 is switched to the non-stopping position without stopping the paper sheet M. In this situation, the paper sheet M is allowed to be fed into the sheet-feeding channel.
The conventional automatic document feeder 1, however, still has some drawbacks. For example, since the swinging arm 110 of the automatic document feeder 1 is swung in response to the friction force, which is generated from the nib between the elastic element 111a and the corresponding coupling element 112. In such way, the elastic element 111a may be suffered from thermal deformation. Due to the rubbing problem for a long time, the elastic element 111a is eventually abraded, and thus the long-term operating stability is deteriorated. In this situation, the use life of the automatic document feeder is shortened.